Honda's OEM vortex generators ... on the Ridgeline pickup mirrors

[MetroMPG]

My brother's got a Honda Ridgeline that he uses for his HVAC business:



(He refused to buy a white panel van like everybody else.)

I noticed it had what looked like VG's on its door mirrors, as you can see in this pic:



At first I thought they were just a useless neato! design element, until I did a bit of digging and found this article:

Another cool feature on the Ridgeline is a "vortex generator" on top of the side mirrors. Don't be fooled by the fancy name. It's nothing more than little plastic ridges molded on top of the mirrors. As the air flows across the mirror, the ridges help to redirect the flow away from the windows.

"We were playing around in the wind tunnel and put some clay on the tops of the mirrors to see what would happen," Keller explained [Ridgeline's assistant large project leader for design]. "The ridges help to hold down wind noise and keep the cabin quieter."

I'm surprised that something as little as these bumps does anything meaningful, aerodynamically. I suppose the mirrors must be out in "clean" flow, so the boundary layer is very thin where the bumps are. Otherwise they'd have no effect.

FYI, they're raised maybe 4 mm. The length of the leading edge is maybe 5-6 mm. I should have put a coin there for reference when I snapped the pics.

[trebuchet03]

Damnit Damnit Damnit...

I have pictures... SOMEWHERE.... of my friend's new rowing oars.... Which have VGs (not unlike those) on the blade.....

I'll find it, eventually :/

Take note everyone... On LOCATION! I've been screaming that for a long time... They are NOT located at trailing edge to do some voodoo "wake fill" magic that hasn't been empirically tested/verified - ever.

[cfg83]

MetroMPG -

Yes, but I think they are more for noise reduction than aero-improvement. Also, you can *buy* these in auto stores in their carbon-bling section. I saw some stick-on ones at a Pep-Boys the other day. I will try to take a pic the next chance I get and post it.

CarloSW2

[tasdrouille]

Everytime I think of vortex generators, I think of golf balls. Have you ever seen the size of the wake of a golf ball versus a smooth sphere? Area wise, it's 4 to 5 times smaller. VGs have been known to keep the flow attached to a surface where it would otherwise separage and create a pressure drag zone.

Now, I don't really understand how they could be noise reducing features in this case. Where does the noise originates from? Does it come from the separation of the flow at the trailling edge of the mirror? If so I could only imagine that these would work by inducing turbulences that disrupt the laminar flow before it meets the low pressure wake.

[donee]

Hi Tasdrouille,

The golf ball thing does not apply here. Unless one puts a clear dimpled cover off the back of the mirror.

That shape of vortex generator creates two vortices on ether side of ridge. The vortex will try to hold shape, but is eventually effected by the vacum behind the mirror. The vortex stretches out behind the mirror creating a flow envelope (not considering the spinning) similar to a boat tail shape. This is because the air has momentum. Once one sets it spinning, it takes time for it to slow down the spinning and go straight again. While the air is spinning, its not tumbling.

[DifferentPointofView]

I've always wondered why people don't put dimples on dead stops like the hatch of a van :/ . Unless the object has to be round... then that wouldn't make sense, but if it does. I'd like to try it.

[tasdrouille]

The golf ball comparison was to illustrate how turbulences can be used to keep flow attached to a surface. Votex generators are basically only "directional dimples" if you will, creating vortices acting as "controlled" turbulence lookalikes.

Even though you provided an explanation on the behavior of the flow, I would like to find out what exactly causes the noise.

IMHO, with the way the vortex generators are designed in the picture, they create as much vortices as turbulences.

[DifferentPointofView]

I have a leaky door, water doesn't get through, but wind noise sure does. wind comes off of the mirror, and some is directed towards the window, causing an aweful noise of wind spinning and flipping in odd directions. it's kinda like when the wind is blowing uber hard outside and you hear it whistling. If you don't have that wind smacking the window and weatherstripping, you have a quieter cabin.

One thing I do like about my leaky weatherstripping is I can use it to help with FE. When it's really loud, I know My FE is gonna be bad. When I get behind a big rig, I know how far back draft from and benefit, because when it stops being loud, I'm drafting good, go too far back, here comes the wind noise...

[MetroMPG]

Originally Posted by DifferentPointofView

I've always wondered why people don't put dimples on dead stops like the hatch of a van :/ . Unless the object has to be round... then that wouldn't make sense, but if it does. I'd like to try it.

"Dead stops" - what's that?

EDIT: regardless, golf ball dimpling doesn't apply to automotive aero for a number of reasons.

[SVOboy]

I think he means when it goes from stuff to no stuff rather quickly,